The present invention relates in general to apparatus for transporting sheets, and more particularly, to a sheet transporting apparatus having a transport belt to which sheets are selectively positively clamped.
In typical reproduction apparatus in commercial use such as copiers, printers, or the like, reliable handling of sheets is essential. Illustratively, in copiers, original information is copied by capturing an image of such information and using such image to produce a copy of such information. The original information may be contained on a document sheet which is placed on a platen for exposure to a light source to form a light image of the information contained thereon, and copies of such information are produced on receiver sheets such as plain bond paper. The document sheets must be carefully handled to prevent damage thereto, and must be reliably positioned for accurate information image acquisition. Further, reliable accurate positioning of the receiver sheets is required to assure that the resultant copies are suitable for their intended use.
In order to more fully utilize the high speed copying capabilities of modern commercial copier apparatus, it is desirable to automatically handle the movement of document sheets to the exposure platen. However, such document sheets can vary widely in size, weight, thickness, and condition. Therefore, it has been difficult to design a document feeder which reliably functions to accurately place the document sheets of all types on the platen without damage to the document sheets. Similarly, receiver sheets may also vary in size, weight, and thickness. Accordingly, feeders for the receiver sheets have also presented design challenges.
With regard to the document transporting device, such device must move the document sheet rapidly to the exposure platen, and must accurately register the document sheet on the platen in a predetermined location to assure production of a complete and acceptable copy. For example, if the document sheet (or the receiver sheet) is skewed or misaligned relative to the predetermined location, the copy will reflect the same skew or misalignment, and may be incomplete or unacceptable in perceived quality by the user. Further, the document transporting device must not damage the original document sheets. If the original document sheet is torn or creased, it may not be of further use to the user, and certainly would not be suitable for subsequent handling by the transporting device.
In transporting either document or receiver sheets, it is common practice to use belts and/or rollers to physically engage the sheets to effect transport thereof. Such physical engagement of the sheets may result in skewing of the transported sheets, and thus improper registration, with the resulting images being created or formed in a manner in which the reproductions are not suitable for their intended use. Other mechanisms for transporting sheets involve clamping the sheets by vacuum to a moving belt, or by a physical clamping mechanism to a chain or drum, and moving the sheet therewith. Such devices provide for a more accurate location of the sheets at various locations over their travel. However, due to the complexity in effecting the clamping action, these devices are complicated in construction and expensive to manufacture.